1. Field of the Invention
The present invention relates to a method of embedding watermark-information so as not to be perceived by the human senses when other information is embedded in digital information, and to a method of reading the watermark-information embedded in the digital information and to apparatus therefor. The term watermark-information is used herein to describe the information to be embedded, due to its analogy to the watermark used to prevent forging of banknotes.
2. Description of the Related Art
The technique of embedding other information into digital information so as not to be perceived by the human senses has now been widely used for the protection of copyright of digital information contents or in systems for preventing false reproduction, by embedding the copyright information, the user ID and the like into the information contents.
With the conventional technique, however, there is a problem in that the embedded information is easily deleted by the lossy compression processing or the compilation processing of the digital information represented by the JPEG (Joint Photograph Expert Group) and the MPEG (Motion Picture Expert Group). Furthermore, since the processing is complicated, it has been difficult to perform embedding and reading of the motion picture and the like on a real-time basis. Assuming that the object in which the information is embedded is, for example, an image, since an area where the luminance change is small is comparatively easily perceived by the human sense, it is difficult to perform embedding without deteriorating the image quality. Moreover, in the lossy compression, the pixel information is deleted in an area where the luminance change is small rather than in an area where the luminance change is large. Therefore, when the lossy compression is performed after the information is embedded with respect to an image having a small luminance change, there is a problem in that the embedded information cannot be read.